Composition and process for the removal of copper during acid cleaning of ferrous alloys

ABSTRACT

A composition and process for the removal of copper compounds during acid cleaning operations of ferrous alloy surfaces wherein a liquid, easily soluble composition is incorporated in the cleaning solution, said composition being the reaction product of (1) an aliphatic or cycloaliphatic aldehyde, (2) an hydroxyethyl amine and (3) thiourea.

United States Patent 11 1 Blair [451 Sept. 23, 1975 COMPOSITION ANDPROCESS FOR THE REMOVAL OF COPPER DURING ACID CLEANING OF FERROUS ALLOYSCharles M. Blair, Fullerton, Calif.

Magna Corporation, Santa Fe Springs. Calif.

Filed: Feb. 26, 1973 Appl. No.: 335,690

Inventor:

Assignee:

U.S. Cl. 252/149; 252/180; 252/80; 134/41; 134/3 Int. Cl. C028 5/06Field of Search 252/149, 180, 80', 210/58; 134/41, 3

References Cited UNITED STATES PATENTS 1/1963 Gardner ..134/4l 2/1963Monroe 252/149 3,164,585 1/1965 Paquette 252/149 3.458.354 7/1969 Reich.v 134/41 3,579,447 5/1971 Mugyczko et a1 134/41 3.803.042 4/1974 Knoxet a1. 252/180 OTHER PUBLICATIONS Loucks, Chemical Engineering/DeskbookIssue/Feb. 26, 1973. pp. 79-84.

Primary ExaminerBenjamin R. Padgett Assistant Examiner-B. Hunt Attorney,Agent, or FirmWilliam C. Norvell, Jr.

[57] ABSTRACT 22 Claims, No Drawings COMPOSITION AND PROCESS FOR THEREMOVAL OF COPPER DURING ACID CLEANING OF FERROUS ALLOYS BACKGROUND OFTHE INVENTION 1. Field of The Invention The present invention relates toa composition and process for the removal of copper encrustations onmetallic surfaces during acid cleaning operations.

2. Description of the Prior Art One of the most commonly encounteredproblems in industrial cleaning of ferrous alloys is that of removingiron oxide and other scale deposits from the surface of ferrousequipment such as those incorporated in steam generators, heatexchangers, boilers. pipeing and similar process equipment. Thesedeposits contain iron oxide, often combined with other inorganicconstituents such as calcium carbonate, magnesium oxide, copper oxideand the like. Complete removal of copper compounds from such encrustedsurfaces is important, but difficult, since the iron present on thesurface acts as a chemical reducing agent causing plating out of anytemporarily dissolved copper, and thus forming a copper coating on theferrous alloy surface. Such copper plating is very undesirable becauseit provides a highly cathodic area which furthers corrosive attack ofany uncoated ferrous alloy surface after the equipment is returned tonormal service. For example, in a high temperature boiler, the presenceof a copper-coated cathodic area can cause greatly acceleratedcorrosion, pitting and devastating failure of nearby ferrous structures.

The removal of copper compounds during cleaning of ferrous equipmentwith acid solutions had been attempted to those skilled in the art usinga number of compositions and processes. For example, hydrochloric acid,sulfamic acid, hydroxy acetic acid or mixtures of hydrochloric acid withother acidic constituents, corrosion inhibitors and wetting agents. arecommonly used for removing and dissolving such scaling depositscontaining copper compounds. Another method of overcoming the problem ofcopper encrustation is presented in US. Pat. No. 2,959,555 wherein it isdisclosed that the inclusion of suitable amounts of thiourea and loweralkyl-substituted thioureas causes the copper to remain in solution inthe hydrochloric acid cleaning compound as a metal complex, allowing thecomplexed copper in solution to be completely'washed out with the acidor spent acid. Although this method does permit the removal of coppercompounds. iron oxide and other scale constituents, it has been found tobe somewhat unsatisfactory in commercial applications. For example,thiourea has very limited solutility in water as well as in hydrocloricacid. Its alkyl derivatives are known to be even less soluble. Puttingthese solid products into solution in an acid during the cleaningprocess becomes a somewhat difficult, tedious and timeconsumingoperation involving solids handling in open solution tanks, stirring orrecirculation of acid to effect solution and, sometimes, even heating ofthe acid. In addition, thiourea and its lower alkyl derivativesgenerally interfere with the action of corrosion inhibitors commonlyused in the acid by those skilled in the art to prevent attack on themetallic alloy structure underlying the iron oxide and otherencrustations. Moreover, the cost of the corrosion inhibitor required isa very significant one, and when thiourea is used even greaterquantities of inhibitor must be employed, thus substantially increasingthe cost of the cleaning operation.

I have now discovered that the disadvantages encountered in the use ofthiourea can now be completely overcome by incorporating in the cleaingsolution a copper complexing agent consisting essentially of l thiourea,(2) an aldehyde selected from the class consisting of aliphatic andcycloaliphatic aldehydes and (3) an hydroxyethyl amine, all ashereinafter disclosed.

The present invention provides a composition and process for the removalof copper-containing compounds during acid cleaning of ferrous surfaces.Specifically it provides for the use in an acidic solution employedduring the cleaning of ferrous surfaces a copper-complexing compositionwhich is in the form of a readily handled liquid and is easily solublein water and acidic solutions. Moreover. this composition is veryeconomical and has been found not to have an adverse effect on theaction of corrosion inhibitors used in the cleaning solution. In fact,the composition herein described has been found to reinforce the effectsof corrosion inhibitors under some conditions, and. in general, to havefewer negative effects on commonly used inhibitors than does thiourea orits lower alkyl derivatives alone.

It is therefore an object of the present invention to provide a processfor the removal of copper depositions on ferrous alloys.

It is also an object of the present invention to provide a compositionfor the removal of copper depositions and encrustations during cleaningoperations of ferrous alloy surfaces of water treatment apparatuses,piping and the like.

It is a further object of the present invention to provide a coppercomplexing agent for use during industrial cleaning operations.

Other objects and advantages in the use of the present composition andprocess will be apparent from the description, examples and claims whichfollow.

SUMMARY OF THE INVENTION A composition and process for the removal ofcopper compounds during acid cleaning operations of ferrous alloysurfaces wherein a liquid easily soluble copper complexing agent isincorporated in the cleaning solution, such agent being the reactionproduct of 1) an aliphatic or cycloaliphatic aldehyde, (2) anhydroxyethyl amine and (3) thiourea.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The composition of the presentinvention may be described in its broadest form as the reaction productof:

a. An aliphatic or cycloaliphatic aldehyde having five carbon atoms orless;

b. An amine having an hydroxyethyl or substituted hydroxyethyl groupattached to an amino nitrogen atom; and

c. Thiourea.

Although the exact formula for the composition of the present inventionis not known, solubility properties and reactivity suggest that thecomposition may be classified as nitriloethoxymethylene thiocarbamates.The multiplicity of possible formulae for compositions of this classmake classification impossible, so I prefer to describe the compositionin terms of suitable reacrants and molar proportions of each.

in order to obtain compositions having the desired solubility andutility, the ratio of the number of carbon atoms in aliphatic orcycloaliphatic substituents in my composition to the number of polargroups therein. such as amino, aldehyde and hydroxyl. should remainbelow about 6-to-l and, preferably. below about 3-to- 1. Further. I havefound that suitable compositions result when the molar equivalent ofaldehyde reactant used is from about 1.0 to about 2.5 times the numberof moles of thiourea and when the molar equivalent of hydroxy present inthe hydroxyethyl amine reactant is also from about 1.0 to about 2.5times the number of moles of thiourea. Additionally, the molarequivalent of hydroxy in the hydroxyethyl amine reactant must be aboutequal to the molar equivalent of aldehyde in the aldehyde reactant.

Aldehydes suitable for use in the synthesis of the present compositioninclude the aliphatic and cycloaliphatic aldehydes containing fivecarbon atoms or less. such as formaldehyde, trioxane, paraformaldehyde,acetaldehydc. propionaldehyde, furfural, glyoxal, glutaraldehyde,acrolein. caproaldehyde and the like. Especially preferred are thosealiphatic and cyloaliphatic aldehydes containing three carbon atoms orless per aldehyde group, such as formaldehyde, acetaldehyde,propionaldehyde, gloyoxal. acrolein and the like. Prolymerie forms ofthese lower aldehydes, such as paraformaldehyde and trioxane, can alsobe utilized since they will serve as a source of monomericaldehyde undernormal reaction conditions. Other polymers such as paraldehyde andmetaldehyde may also be successfully utilized.

Amines suitable for use in preparing the present com position are thealiphatic amines having at least one hydroxyethyl or substitutedhydroxyethyl group attached to the amino nitrogen. The preferred aminereactant should not contain so many hydrocarbon constituents as torender the final composition insoluble or difficultysoluble in water oracidic cleaning solutions. Preferred amines will contain less than aboutseven carbon atoms per amino nitrogen atom and especially preferredreactants will contain only two or three carbon atoms per amino nitrogenatom. Examples of suitable amine reactant include Z-hydroxypropylamine,monethanolamine, diethyl monoethanolamine. methyl diethanolamine.triethanolamine, hydroxyethylethylene diamine. di-2- hydroxypropylamineand the like.

The reaction of the aldehyde and amine reactants with thiourea may becarried out simply by mixing the reagents and warming slightly whilestirring until the solid thiourea disappears and a homogeneous, liquidproduct is obtained. Usually, however. it will be preferred toincorporate some water into the reaction mixture and to add an organicor inorganic acid in an amount at least equivalent to about one-fifth ofthe amine present. The acid may be added before. during or near the endof the reaction period. Suitable acids for use with the presentcomposition include acetic acid, hydrochloric acid, sulfuric acid andphosphoric acid in concentrations of from between about and about 25%.The use of acetic acid is preferred.

Completion of reaction is generally marked by dissolution of thethiourea and formation of a clear. homogeneous liquid of a deepyellowish or reddish color. Typically, the temperature is brought toabout 90C and held for one hour to effect reaction although with higherboiling or less reactive reagents, the temperature may be raised abovethis point. as. for example. to 150C.

The following examples further illustrate the preparation of the presentcomposition.

EXAMPLE I 76 grams of thiourea and 50 grams of thiethanolamine wereplaced in a 500 ml. three-neck flask fltted with stirrer. refluxcondenser, thermometer and exterior heating mantle. While stirring atroom temperature, 210 grams of 30% aqueous glyoxal were added over aperiod of one hour. 20 grams of acetic acid were then added over alO-minute period during which time the temperature rose to about 35C.The heating mantle was then activated and the temperature increased to95C and held for 1 hour. The resulting composition was a viscous redoil, soluble in water, 5% hydrochloric acid and dilute alkali.

EXAMPLE ll 76 grams of thiourea and 50 grams of triethanolamine werecombined in a flask equipped as in Example l. While stirring at roomtemperature, 8] grams of 377: formalin solution (methanol-free) werequickly added to the mixture in the flask. 25 grams of acetic acid werethen added over a 30-minute period during which the temperature rose toabout 40C. The temperature was then raised to 1 10C and held for 30minutes. The resulting clear. red oil was soluble in water and 5'71hydrochloric acid. The pH of a 10% solution of this composition indistilled water was 5.4.

EXAMPLE [I] 104 grams of hydroxyethethylenediamine were substituted forthe triethanolamine used in Example ll. The resulting red oil dissolvedreadily in water and a 10% solution thereof had a pH of about 8.5. Thiscomposition was also readily soluble in both acidic and alkalinesolutions.

EXAMPLE IV 76 grams of thiourea, 150 grams of furfural and lOO grams ofwater were combined in a l-liter flask equipped as in Example l. lOOgrams of isopropanola mine were then slowly added to the flask contentswhile stirring. A small exotherm was noted. grams of l07( aqueoushydrochloric acid were then added over a 1- hour period. The temperaturespontaneously rose to about 50C and was then raised to 105C by externalheating. lt was held at this temperature for about 25 minutes. Theresulting composition resembled that of Example III in physicalproperties.

EXAMPLE V 6l grams of thiourea. 74 grams of monoethanolamine and 40grams of water were placed in a flask as in Example I. While stirringthis mixture, 66 grams of chilled acetaldehyde were added in 5 gramincrements. The incremental additions took place over one hour duringwhich a mild exothermic reaction raised the temperature from 25C to 32C.16 grams of acetic acid were then added to the reactant and heat slowlyapplied in order to raise the temperature to l 14C. The reactants werestirred and held at this temperature for minutes. The resulting red oilcomposition was very soluble in water and acids in aqueous solutions.

EXAMPLE V] EXAMPLE VII 61 grams of thiourea, 74 grams ofmonoethanolamine and 40 grams of water were reacted in a flask as inExample 1. The flask was held in a water bath at a temperature of about25C. While stirring the reaction in the flask, 220 grams of 40% aqueousglyoxal were added to the reactants incrementally over a period ofminutes. The water bath .was replaced by a heating mantle and the flaskcontents were then brought to and held at 85C for 1 hour and minutes.The product was a mobile red oil, readily soluble in water and aqueousacids.

EXAMPLE Vlll The following test solution was prepared:

CuCl 0.12892 Crude Pyridine Corrosion Inhibitor 0.4% HCl 5.0% Water tomake 100.0%

Steel coupons measuring about 1V2 inch X /2 inch Vs inch were immersedin 50 ml. of the above solution containing a known amount of the presentcomposition made according to the above Examples. The bottles containingthe solution and coupon were held in a water bath at 70C for 3 hours.The solutions were ob served immediately after adding the compositionand the coupons were removed and examined after the test period. Theresults of these tests using the composition of the present inventionare given in Table 8 below, along with the results obtained using onlythiourea.

ple V1. The coupons were reweighed after test exposure and chemicalremoval of any deposited copper. Corrosion rates were computed from theweight loss, time of exposure and coupon dimensions and are presentedbelow in Table 9 (in unites of "mils per year which is defined asthousandths of an inch penetration per year (MPY)).

Table 9 Corrosion Rate of Weighed Steel Coupons in H drochloric AcidSolution These results demonstrate the increasingly beneficial effect ofthe additive. composition and process of the present invention inreducing the corrision rate as higher concentrations are employed.Thiourea. in contrast, shows a corrosion rate slightly exceeding theblank (None") rate when present at a 2.07r concentration. Normalcommercial use concentrations may equal or exceed 2.0% in many cases.

EXAMPLE X Actual application of the present invention in an industrialcleaning operation is relatively simple and is exemplified by the log ofa boiler cleaning operation. The boiler to be cleaned was a Babeock andWilcox fire tube model having a volumetric capacity on the water side of15,000 gallons and constructed of carbon steel. Cleaning of the heaterwas necessary to remove iron oxides, silica, copper oxides and otherorganic and inorganic scale constituents. The boiler was first given anTable 8 Concentration in Appearance Appearance of Coupon Product UsedTest Solution Of Solution After 3 Hours. at 70C Example 2 1.871 slightlycloudy slight Copper deposit 2 3.0 clear no deposit of copper Example 42.0 flocculant precipisome deposit of copper tate 4 3.2 traceprecipitate trace of copper Example 5 1.2 fine fluffy precipiheavycopper tale 5 1.6 trace of precipitate no copper 5 2.0 very clear nocopper Thiourea 0.6 flocculant moderate copper deposit precipitate 0.8clear no copper EXAMPLE [X alkaline wash by circulating through thetubes and drum while firing to a temperature of about 190F, 15,000gallons of an aqueous solution containing 300 gallons of caustic soda,1,800 pounds of soda ash and 5 gallons of hydrazine. This solution wascirculated for 15 hours after which heating was stopped and the spentsolution drained and discharged. The bottom headers and drum wereflushed with water to remove alkaline solution and loose deposits. Anacid solution was then prepared containing 2.100 gallons of 32%commercial hydrochloric acid, 990 pounds of ammonoum bifluoride. 100pounds of citric acid. gallens of crude alkyl pyridine, 1200 pounds ofthe product of Example V, and sufficient water to bring the total volumeto slightly over 15,000 gallons. The boiler was then filled with theacid solution which was heated to 190F and circulated for 6 hours.Firing was stopped and the spent acid was drained from the boiler afterwhich the heater was filled with a soda ash neutralizing solutioncontaining 100 pounds of soda ash per 1,000 gallons of water. Thissolution was then drained. The boiler was blown down with dry nitrogenpreparatory to being put back in service.

An analysis of the spent acid indicated that the quantity of scaleconstituents removed in the true solution was as follows:

Silica 53.5 pounds Copper l07.0 pounds Iron 1.759 pounds Visualinspection of the interior boiler surface showed a greyish metallicsurface which was free of scale deposits. The boiler surface was alsorust resistant.

The ability of the present composition to hold copper in solution isclearly shown by the above results In comparing amounts required foroptimum results it should carefully be noted that the products ofExamples 1 through Vll are diluted with water and are not 100% active.Thiourea, in contrast. is a I009: active solid.

Much of the utility of the present composition is attributable to thefact that it is an aqueous solution of high activity which can bepumped, poured. mixed and easily dissolved in acidic cleaning solutions.

The amount of the composition which is required for holding copper insolution varies with the amount of copper in any given system to becleaned and with the particular composition to be used. Generallyspeaking. an amount of the composition which will provide from about L8to about 2.0 pounds of sulphur for every pound of copper ion in thesystem will achieve very satisfactory results. ln contrast. wherethiourea is used, an amount sufficient to provide at least 2.5 pounds ofsulphur is generally necessary to prevent precipitation and copperdeposition. Thus. an obvious advantage in the use of the presentcomposition is readily apparent.

Since the amount of copper in the system strongly affects the requiredamount of the present composition. it becomes very important to makecareful analysis of the scale and impurities in the system to be cleanedand to estimate as carefully as possible the amount of copper present.This is frequently difficult to accurately ascertain. It is preferableto use slightly more of the present composition than might be indicatedby preliminary testing and the like. Under some abnormal conditions, itmay desirable to utilize amounts of the present composition suffieientto provide up to 5 pounds of sulphur per pound of copper. Use of toolittle of the composition results in the formation of insolublecomplexes of copper and composition. In such mixtures, plating out ofcopper may still be prevented. However, unless high fluid velocities andgood turbulence are present during draining of the acid cleaningsolution, subsequent flushing and neutralization. some precipitate maybe left in the system to act as a source of copper in the futureoperations. For this reason it is desirable to use sufficient amounts ofthe present invention in order to prevent formation of anycopper-containing cloud or precipitate.

The use of more of the present composition than is required by thecopper present in the system is, of course. undesirable from an economicviewpoint. Still further, the use of increased amounts of the presentcomposition will sometimes also require the addition of more corrosioninhibitor. which further increases cost. This is particularly true withthiourea which has a generally negative effect on inhibitor performance.The composition of the present invention, in contrast. has less effecton inhibition and does, in some instances, actually improve inhibitorperformance.

Although the invention has been described in terms of specifiedembodiments which are set forth in detail. it should be understood thatthis is by illustration only and that the invention is not necessarilylimited thereto, since alternative embodiments and operating techniqueswill become apparent to those skilled in the art in view of thedisclosure. Accordingly. modifications are contemplated which can bemade without departing from the spirit of the described invention.

1 claim:

1. An additive for use in compositions for the removal of copperencrustations encountered during acid cleaning operations of ferrousalloy surfaces consisting essentially of the reaction product of a. analiphatic or cycloaliphatic aldehyde having five carbon atoms or less;

b. an amine having an hydroxyethyl or substituted hydroxyethyl groupattached to an amino nitrogen atoms: and

c. Thiourea. the ratio of carbon atoms in the aliphatic orcycloaliphatie substituents to the number of polar groups therein beingno greater than about S-to-l. the molar equivalent of aldehyde beingbetween about l.0 and about 2.5 per mole of thiourea. the molarequivalent of hydroxy present in the amine being from about 1.0 to about2.5 times the number of moles of thiourea, and the molar equivalent ofhydroxy being equal to the molar equivalent of aldehyde.

2. The additive of claim 1 wherein the ratio of carbon atoms in thealiphatic or cycloaliphatic substituents to the number of polar groupstherein is below about 3-tol.

3. The additive of claim 1 wherein the aldehyde is selected from theclass consisting of formaldehyde. trioxane, paraformaldehyde.acetaldehyde. propionaldehyde. furfural glyoxal, gluteraldehyde,acrolein and caproaldchyde.

4. The additive of claim 1 wherein the aldehyde is selected from theclass consisting of paraformaldehyde. trioxane. paraldehydc andmetaldehyde.

5. The additive of claim 1 wherein the amine contains less than about 7carbon atoms per amino nitrogen atom.

6. The additive of claim 1 wherein the amine contains three carbon atomsper amino nitrogen atom.

7. The additive of claim 1 wherein the amine contains about two carbonatoms per amino nitrogen atom.

8. The additive of claim 1 wherein the amine is selected from the classconsisting of Z-hydroxypropylamine. monoethanolamine, diethylmonoethanolamine. diethanolamine, methyl diethanolamine.triethanolamine. hydryoxyethylethylene diamine anddi-2-hydroxypropylamine.

9. A composition for the removal of copper compounds during acidcleaning operations of ferrous alloy surfaces consisting essentially ofan aqueous solution of an acid and the additive of claim 1, the ratio ofacid in said composition to the amine in the additive being at least ashigh as about l-toby volume.

10. The composition of claim 9, wherein the acid is an organic acid.

11. The composition of claim 9 wherein the acid is an inorganic acid.

12. The composition of claim 9 wherein the acid is selected from theclass consisting of acetic, hydrochloric. sulfuric and phosphoric.

13. The composition of claim 9 wherein the acid is acetic.

14. A process for the removal of copper encrustations on ferrous alloysurfaces comprising the steps of:

a. Contacting the ferrous surface with an aqueous solution of l) theadditive of claim 1 in an amount sufficient to provide from about 1.8 toabout 5.0 pounds of sulphur for each pound of copper ion, and (2) anacid selected from the class consisting of acetic, hydrochloric,sulfuric and phosphoric, the amount of acid in said solution being aratio to the amine in the additive of at least as high as about l-to-5by volume; and

b. Maintaining contact with the said ferrous surface by the said aqueoussolution for a time sufficient to substantially solubilize the saidcopper encrustation.

15. The process for the removal of copper encrustations on ferrous alloysurfaces comprising the steps of:

a. Contacting the ferrous surface with an squeous solution of anadditive consisting essentially of the reaction product of I) analdehyde having five carbon atoms or less selected from the classconsisting of aliphatic and cycloaliphatic aldehydes, (2) an aminehaving a hydroxyethyl or substituted hydroxyethyl group attached to anamino nitrogen atom, and (3) thiourea. said additive being present in anamount sufficient to provide from about 1.8 to about 5.0 pounds ofsulphur for each pound of copper present. and an aqueous acidic solutioncomprising an acid selected from the class consisting of acetic,hydrochloric, sulphuric, and phosphoric acids; and

b. Maintianing contact with said ferrous surface by the said aqueousacidic solution having present therein the said additive for a timesufficient to solubilize substantially all of said encrustation.

16. The process of claim 15 wherein the aldehyde is selected from theclass consisting of formaldehyde. trioxane, paraformaldehyde,acetaldehyde, propionaldehyde, furfural, glyoxal, fluteraldehyde,acrolein and caproaldehyde.

17. The process of claim 15 wherein the aliphatic or cycloaliphaticreactant contains less than four carbon atoms per aldehyde group.

18. The process of claim 15 wherein the aldehyde is selected from theclass consisting of paraformaldehyde, trioxane, paraldehyde andmetaldehyde.

19. The process of claim 15 wherein the amine contains less than aboutseven carbon atoms per amino nitrogen atom.

20. The process of claim 15 wherein the amine contains 3 carbon atomsper amino nitrogen atom.

21. The process of claim 15 wherein the amine contains about two carbonatoms per amino nitrogen atom.

22. The process of claim 15 wherein the amine is selected from the classconsisting of Z-hydroxypropylamine. monoethanolamine, diethylmonoethanolamine, diethanolamine. methyl diethanolamine,triethanolamine, hydroxyethylethylene diamine and di-2-hydroxypropylamine.

1. AN ADDITIVE FOR USE IN COMPOSITIONS FOR THE REMOVAL OF COPPERENCRUSTATIONS ENCOUNTERED DURING ACID CLEANING OPERATIONS OF FERROUSALLOY CONTAINING ESSENTIALLY OF THE REACTION PRODUCT OF A. AN ALIPHATICOR CYCLOALIPHATIC ALDEHYDE HAVING FIVE CARBON ATOMS OR LESS: B. AN AMINEHVING AN HYDROXYETHYL OR SUBSTITUTED HYDROXYETHYL GROUP ATTACHED TO ANAMINO NITROGEN ATOMS: AND C. THIOUREA, THE RATIO OF CARBON ATOMS IN THEALIPHATIC OR CYCLOALIPHATIC SUBSTITUENTS TO THE NUMBER OF POLAR GROUPSTHEREIN BEING NO GREATER THAN ABOUT 5-TO-1, THE MOLAR EQUILAVENT OFALDEHYDE BEING BETWEEN ABOUT 1.0 AND ABOUT 2.5 PER MOLE OF THIOUREA, THEMOLAR EQUILAVENT OF HYDROXY PRESENT IN THE AMINE BEING FROM ABOUT 1.0 TOABOUT 2.5 TIME THE NUMBER OF MOLES OF THIOUREA, AND THE MOLAR EQUILAVENTOF HYDROXY BEING EQUAL TO THE MOLAR EQUILAVENT OF ALDHYDE.
 2. Theadditive of claim 1 wherein the ratio of carbon atoms in the aliphaticor cycloaliphatic substituents to the number of polar groups therein isbelow about 3-to-1.
 3. The additive of claim 1 wherein the aldehyde isselected from the class consisting of formaldehyde, trioxane,paraformaldehyde, acetaldehyde, propionaldehyde, furfural, glyoxal,gluteraldehyde, acrolein and caproaldehyde.
 4. The additive of claim 1wherein the aldehyde is selected from the class consisting ofparaformaldehyde, trioxane, paraldehyde and metaldehyde.
 5. The additiveof claim 1 wherein the amine contains less than about 7 carbon atoms peramino nitrogen atom.
 6. The additive of claim 1 wherein the aminecontains three carbon atoms per amino nitrogen atom.
 7. The additive ofclaim 1 wherein the amine contains about two carbon atoms per aminonitrogen atom.
 8. The additive of claim 1 wherein the amine is selectedfrom the class consisting of 2-hydroxy-propylamine, monoethanolamine,diethyl monoethanolamine, diethanolamine, methyl diethanolamine,triethanolamine, hydryoxyethylethylene diamine anddi-2-hydroxypropylamine.
 9. A composition for the removal of coppercompounds during acid cleaning operations of ferrous alloy surfacesconsisting essentially of an aqueous solution of an acid and theadditive of claim 1, the ratio of acid in said composition to the aminein the additive being at least as high as about 1-to-5 by volume. 10.The composition of claim 9, wherein the acid is an organic acid.
 11. Thecomposition of claim 9 wherein the acid is an inorganic acid.
 12. Thecomposition of claim 9 wherein the acid is selected from the classconsisting of acetic, hydrochloric, sulfuric and phosphoric.
 13. Thecomposition of claim 9 wherein the acid is acetic.
 14. A process for theremoval of copper encrustations on ferrous alloy surfaces comprising thesteps of: a. Contacting the ferrous surface with an aqueous solution of(1) the additive of claim 1 in an amount sufficient to provide fromabout 1.8 to about 5.0 pounds of sulphur for each pound of copper ion,and (2) an acid selected from the class consisting of acetic,hydrochloric, sulfuric and phosphoric, the amount of acid in saidsolution being a ratio to the amine in the additive of at least as highas about 1-to-5 by volume; and b. Maintaining contact with the saidferrous surface by the said aqueous solution for a time sufficient tosubstantially solubilize the said copper encrustation.
 15. The processfor the removal of copper encrustations on ferrous alloy surfacescomprising the steps of: a. Contacting the ferrous surface with ansqueous solution of an additive consisting essentially of the reactionproduct of (1) an aldehyde having five carbon atoms or less selectedfrom the class consisting of aliphatic and cycloaliphatic aldehydes, (2)an amine having a hydroxyethyl or substituted hydroxyethyl groupattached to an amino nitrogen atom, and (3) thiourea, said additivebeing present in an amount sufficient to provide from about 1.8 to about5.0 pounds of sulphur for each pound of copper present, and an aqueousacidic solution comprising an acid selected from the class consisting ofacetic, hydrochloric, sulphuric, and phosphoric acids; and b.Maintianing contact with said ferrous surface by the said aqueous acidicsolution having present therein the said additive for a time sufficientto solubilize substantially all of said encrustation.
 16. The process ofclaim 15 wherein the aldehyde is selected from the class consisting offormaldehyde, trioxane, paraformaldehyde, acetaldehyde, propionaldehyde,furfural, glyoxal, fluteraldehyde, acrolein and caproaldehyde.
 17. Theprocess of claim 15 wherein the aliphatic or cycloaliphatic reactantcontains less than four carbon atoms per aldehyde group.
 18. The processof claim 15 wherein the aldehyde is selected from the class consistingof paraformaldehyde, trioxane, paraldehyde and metaldehyde.
 19. Theprocess of claim 15 wherein the amine contains less than about sevencarbon atoms per amino nitrogen atom.
 20. The process of claim 15wherein the amine contains 3 carbon atoms per amino nitrogen atom. 21.The process of claim 15 wherein the amine contains about two carbonatoms per amino nitrogen atom.
 22. The process of claim 15 wherein theamine is selected from the class consisting of 2-hydroxy-propylamine,monoethanolamine, diethyl monoethanolamine, diethanolamine, methyldiethanolamine, triethanolamine, hydroxyethylethylene diamine anddi-2-hydroxypropylamine.